Pronation itself is not wrong as we need to pronate and supinate as part of our gait. Pronation (rolling in) acts as a shock absorbing process and supination (rolling out) helps to propel our feet forward.
Over-pronation occurs when we pronate too deep and for too long, not giving the foot a chance to 'recover' and supinate.
Excessive pronation hampers our natural walking pattern, causing an imbalance and leading to wear and tear in other parts of the body, with every step we take! Whether you have a true flat foot or suffer from over-pronation in both cases your poor walking pattern may contribute to a range of different complaints. Especially with age, poor alignment of the feet will cause very common conditions such as Heel Pain or Knee Pain.
Over-pronation has different causes. Obesity, pregnancy, age or repetitive pounding on a hard surface can weaken the arch leading to over-pronation. Over-pronation is also very common with athletes, especially runners and most of them nowadays use orthotics inside their shoes.